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Question about Watts?

06-18-2009, 01:34 PM

I'm thinking of putting a few solar panels up on my roof. just for times when we have a power failure overnight. I want to power a 12 volt tv that draws 18 watts at 12 volts. so, do i just say 18x the amount of hours that I want to power the TV?

I'll have a 220 watt panel and get about 4 hrs of sunlight where it will be placed, I know I need a charge controller to regulate the voltage, as the the panel puts out 17 volts.

I also will use a few batteries to store the watts that the panel produces.

your battery will be rated in amp hrs, which is watts / voltage= amps, and how may amps it may discharge at for a given time.

http://www.windpowerunlimited.com/ba.../Amp_Hours.htm
If you have never dealt with deep cycle batteries, you may have run across the term “Amp Hours” abbreviated Ah. This term is used to express the storage capacity of deep cycle batteries. This is the maximum sustained amperage drawn from a fully charged battery over a certain time period to a point where the battery is at 100% DOD (depth of discharge), for all purposes dead! This amperage is then multiplied by the discharge period to give the battery its Ah rating. The period of time used to drain and measure the battery is usually 20 hours, although longer or shorter time periods may be used depending on the application.

one other thing you never want to discharge your battery bank over 50%.
preferable less,

And on charging never estimate 100% of the exposed time of the sun on the panels, as the controller is not 100% efficient, and more than likely the batteries will taper off as they charge in the amount they will take when they nearing fully charged. and your battery is not 100%,
use deep cycle batteries.

Push sticks/blocks Save Fingers
~~~~~~~~~~~~~~~~~~~
"The true measure of a man is how he treats someone who can do him absolutely no good."
attributed to Samuel Johnson
~~~~~~~~~~~~~~~~~~~
PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

one other thing you never want to discharge your battery bank over 50%.
preferable less,

And on charging never estimate 100% of the exposed time of the sun on the panels, as the controller is not 100% efficient, and more than likely the batteries will taper off as they charge in the amount they will take when they nearing fully charged. and your battery is not 100%,
use deep cycle batteries.

Thanks BHD, I've just started reading up on the solar thing. I'm just trying to get the math part down first. I've got a KIL-O Watt reader coming in the mail to check the wattage draw on the Items I want to run.

I'm so glad I've asked around in here and another place. I would have been thinking I would get full power from my panels and battery.
Kinda stinks all the wattage you lose through the sysyem.

Thanks for your help and the links, they're very useful to me.
I started out all pumped to get it started but, now I'm going to have to keep reading before I get too far ahead of myself.

sigpic

Comment

Is the only electrical device you want to power the tv? what kind and size of tv is it? It might be possible to find a more efficient small flat panel tv, and reduce your needs for solar panel size and battery capacity. It might be cheaper to do that if the efficiency difference is high enough.

Comment

Is the only electrical device you want to power the tv? what kind and size of tv is it? It might be possible to find a more efficient small flat panel tv, and reduce your needs for solar panel size and battery capacity. It might be cheaper to do that if the efficiency difference is high enough.

I've found a 12 volt tv that only uses 18 watts, and i will be using other items too...still trying to figure things out...

Comment

just a thought,
I did think of using the solar thing to power some lights in my cellar, and did the math and so on and came to the conclusion a led camping lantern was the better investment,
as it could run up to two weeks continuously on 4 d batteries,

you may find that pulling the battery out of a car or running a cord with two alligator clips on it to the car, may be a much cheaper alternative and then if the outage lasts for a little longer time start the car and let it recharge the battery up. (or keep a battery deep cycle, on a trickle charger in the garage and run a line to it to run the TV, if need to recharge one could start a car and hook up some jumper cables to charge it.

if your wanting a extend charger a small horse power gas motor and a car alternator belt drive by the motor and some leads for charging the battery and the dividend of this is you can charge a car battery if necessary as well power or no power, use a GM one wire alternator with the built in regulator and your in business,
similar to this, http://theepicenter.com/tow082099.html or http://theepicenter.com/tow02077.html

been thinking of making one of my own for some time now, I have all the suff just would need to assemble it.

fuse the line to the TV for its and your safety, 12 volt battery may not be much voltage but it can really put out the amps and wires can glow red in a fraction of a second if some thing is not right,

Push sticks/blocks Save Fingers
~~~~~~~~~~~~~~~~~~~
"The true measure of a man is how he treats someone who can do him absolutely no good."
attributed to Samuel Johnson
~~~~~~~~~~~~~~~~~~~
PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

Comment

just a thought,
I did think of using the solar thing to power some lights in my cellar, and did the math and so on and came to the conclusion a led camping lantern was the better investment,
as it could run up to two weeks continuously on 4 d batteries,

you may find that pulling the battery out of a car or running a cord with two alligator clips on it to the car, may be a much cheaper alternative and then if the outage lasts for a little longer time start the car and let it recharge the battery up. (or keep a battery deep cycle, on a trickle charger in the garage and run a line to it to run the TV, if need to recharge one could start a car and hook up some jumper cables to charge it.

if your wanting a extend charger a small horse power gas motor and a car alternator belt drive by the motor and some leads for charging the battery and the dividend of this is you can charge a car battery if necessary as well power or no power, use a GM one wire alternator with the built in regulator and your in business,
similar to this, http://theepicenter.com/tow082099.html or http://theepicenter.com/tow02077.html

been thinking of making one of my own for some time now, I have all the suff just would need to assemble it.

fuse the line to the TV for its and your safety, 12 volt battery may not be much voltage but it can really put out the amps and wires can glow red in a fraction of a second if some thing is not right,

Holy smokes BHD, I'm glad I've meet you and the mower into a generator is one slick Idea. I'm a person that likes to tinker with everything myself.

Here in Florida the summer is a killer with no power. last time we only had a 2.5 portable TV screen to watch, terrible really. It's so damn hot with out AC too.....got to have some sort of fan moving and a few lights.

The refrigerator was a big problem also.

I'm just not going to get caught with my pants down this season, hopefully...

at first were talking about a TV at 18 watts 12 volt if I read correctly, and a battery and solar panels,

now were up to refrigerators and AC, were talking apples and oranges as far as power usage.

the power requirements of the last two items will not function with any realistic length of time nor will the "lawn mower generator" have any were near the power either in Horse power or in electrical power, to be able to supply a refrigerator or a AC unit of any size, (house sized appliances),
yes there are some Mini refrigerators or even now "solar rated" refrigerators, (very low power usage, and small capacity and usually a chest type configuration), I know of no AC that is practical on minimal power usage,

for the refrigerator and the AC, one is going to have to step up to a good sized generator in the 120/240 voltage and I would guess a min, of 4000 watts of running power, (surge power is more sales hype and any thing), to start a electric motor min figure it needs a min, of 2 times the run amps, and depending on the construction of the motor and type, it could be up to 6 times the run amps, and that needs to be figured in to the generators capacity, so your AC and your refrigerator will need much more than the "lawn mower generator" and a 12 volt battery,

if one is thinking of using an inverter to run 120 volt appliances, if it says it takes 2 amps, at 120 it will pull 20 amps + going into a 12 volt inverter,

and if using an inverter it would need to be sized for the motor starting loads if there are motors involved with them,

If one wants to run the Refrigerator and or the AC, the rate of electrical usage, one would be running some type of gas motor continuously, (120/240 volt generator) or the (lawn mower generator) to keep the battery charged to any reasonable level.

If one is wanting to use some type of battery bank to supply your emergency power needs one is going to have to be fairly choosy on the loads he supplies, unless your willing to put in a few thousand dollar battery bank, (I have been looking at wind turbines, and if I would do a off grid system for my place, the turbine would be in the 20 to 50 thousand range, and to be off grid I would have to invest a similar amount for a battery banks, for my place to live as I live now,

not saying your trying or wanting to live like "normal", but when on the grid we have the advantage (Illustration) the grid is like being pulled down the road by huge semi truck, when we go to a portable small generator, we drop down to a small riding lawn mower, if were careful it will do us a good job if we do not over load it, If we go to solar, we have a motorized skate board,
the lawn mower generator is maybe a motorized bicycle in comparison.
so we need to watch very carefully what kind of load we plan on pulling with it.

it is not that running AC or refrigeration off of batteries can not be done, but I think it will take more than what your currently thinking and a set up that is not feasible for the cost benefit,
and running a small portable generator for even 8 hrs a day becomes a fairly expensive ordeal, as they (4000 watt unit will probably burn 1/2 to a gallon an hr depending on make and load), are not that fuel economical. (unless one steps up to a very slow RPM diesel powered unit, similar to listeroid diesel engine http://www.listeroid.com/ ),

Push sticks/blocks Save Fingers
~~~~~~~~~~~~~~~~~~~
"The true measure of a man is how he treats someone who can do him absolutely no good."
attributed to Samuel Johnson
~~~~~~~~~~~~~~~~~~~
PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

Comment

I do have a 5000 watts regular generator for the real long periods of no power.

My thinking on the solar panel is this.

The area where I live has many trees that hang over the power lines (above ground). a Few times a year wind or whatever takes a tree limb out and there goes the power. the power company takes too long for me to get it resolved so, I thought I would use the solar power with battery storage to run the 12 volt TV, 12 fan and a few lights. I know it wont power the AC or my well pump or refrigerator.

The thinking behind this is, it's too much work to crank the generator up for these little outages. so I'll just use the solar system for these, then maybe power some outside lights the rest of the time to get more use of the solar panel.

good thing is I'll have the combo of the two in hard times. as long as the panel doesn't get sucked off the roof in the storm . think I'll make it removeable for this matter too.

Comment

Here are a few quickies from someone who has over $18,000 invested in battery bank, chargers, etc...

1) Don't believe the numbers! A 1,000 watt panel will give you a max of about 80% during peak sunlight with proper aiming and a clean cover. You'll lose some of that to the converters, controllers, wiring, etc.

2) The surge required by motors will get you! Either our fridge or our freezer can start, but not both. Despite the fact that each is on a separate 6,000 watt inverter.

3) Use either a 24-volt or 48-volt system, not 12-volts.

4) Our battery bank was designed to run the house for 6 days (using the numbers). It will make it 3 days, but only with strict power control measures.

Comment

Here are a few quickies from someone who has over $18,000 invested in battery bank, chargers, etc...

1) Don't believe the numbers! A 1,000 watt panel will give you a max of about 80% during peak sunlight with proper aiming and a clean cover. You'll lose some of that to the converters, controllers, wiring, etc.

2) The surge required by motors will get you! Either our fridge or our freezer can start, but not both. Despite the fact that each is on a separate 6,000 watt inverter.

3) Use either a 24-volt or 48-volt system, not 12-volts.

4) Our battery bank was designed to run the house for 6 days (using the numbers). It will make it 3 days, but only with strict power control measures.

5) This is a very expensive adventure.

Hey Luci, thanks for your input. I'm really interested in the reason behind not using 12 volts. can you explain it a little more?

Thanks..

sigpic

Comment

Don't have a good answer for the higher voltages question, though it's probably related to safety and efficiency. As was mentioned, if you're talking about fridges and AC, you will need a good inverter, and try to get clean power to your appliances because of the large current draw that the motors have when they kick on. During an outage, if you hook up your fridge to a standard backup generator that doesn't condition the power, it will shorten the useful life of your appliances.

As for other alternatives, I've heard stories of people getting pretty good results from using Toyota Priuses' hybrid engine as a back up power source. Once hooked into the electrical, the appliances run off the battery bank. When they get low, the Prius will turn on the gas engine to start recharging it. Anyone out there with thoughts / experience with this?

Comment

Don't have a good answer for the higher voltages question, though it's probably related to safety and efficiency. As was mentioned, if you're talking about fridges and AC, you will need a good inverter, and try to get clean power to your appliances because of the large current draw that the motors have when they kick on. During an outage, if you hook up your fridge to a standard backup generator that doesn't condition the power, it will shorten the useful life of your appliances.

As for other alternatives, I've heard stories of people getting pretty good results from using Toyota Priuses' hybrid engine as a back up power source. Once hooked into the electrical, the appliances run off the battery bank. When they get low, the Prius will turn on the gas engine to start recharging it. Anyone out there with thoughts / experience with this?

Yes, the Priuses is a great Idea....just don't have one myself.

The system I'm thinking of building is a back up only, so 12 volts is OK for me to start out with, I'm still learning.

From the info I gathered so far, It looks like a small back up system is a lot of cash to put out though. If the dang PV panels just didn't cost so much..

I hope they get those Nano cell panels going one day. They're supposed to be about a dollar per watt.

Comment

the conversion rate from 12 volts to 120 volts when you do the amps is a killer on the amps,

you have a battery bank that is 12 volts, you have an inverter that is 120 volts, that is 10 times, the same conversion is for the amps but the other way, Using Lucy's example if they pull the full 6000 watts, of power from the inverter, at 120 volts is 50 amps of out put, that is 500 amps of draw out of the 12 volt battery's at once, that is a fairly heavy draw down, that is some huge cables, That tis more than a huge diesel engine starter motor pulls on the starter on a cold morning,
so if you have battery bank of 48 volts of you have reduced the draw out of the battery bank to 125 amps, a bank of 24 volts would be 250 amps of draw, the size of things in the inverter can be smaller and less expensive, If your pulling 500 amps out of a battery you could litterly melt the battery down in to lead ingots, if you have any corrosion you will have heat or reduction of flow and problems, in addition the wires have to be huge, and the components massive,

the problem comes when you start to mix produced for the grid, AC appliances with DC stuff, one needs an inverter, to transform the voltages and to make the sine wave,

in the good Ole days, they had a 36 volt standard and made 36 volt DC appliances but REA (rural electrical power) came in and destroyed the original wind energy industry that was built in a 36 volt standard, yes there was 6 volt for radio battery charging and some 12 volts systems,
but the bigger systems were 36 volt,and they were making appliances in that voltage, but 1930 appliances were not that many,

if your just going to run a small RV fan and a simple TV off of the battery direct, I would not be concerned with any other voltage, but if you want to set up a system for the refrigerator and other you will need like said a hefty battery bank and huge inverter, and if your look into that they plan in the higher voltages, (at $18,000) you can conclude that Lucy has a large battery bank, just guessing but I would guess that Lucy's system has L16 batteries in it that are 6 volt and cost some where in the $200 to $400 each and probably have a bank of about 48 of them, tied together, http://www.solardyne.com/trojdeepcycb1.html probably 8 batteries per string to make the 48 volts, and 6 stings of them to make up the bank, Possibly 8 strings of them,

for battery life the less one has to discharge them the better off one is.

large solar or battery systems are complicated and expensive and management of them is critical and one other factor even using industrial batteries and proper management you still working on a limited life, of about 10 years 15 if your have been really good to them, and you can destroy the bank if you let it set discharge for a short time,
if you look at the URL I posted it stated a 20% discharge
any more really starts to cut in to life on the battery's, and if you read there life is only saying 3 to 6 years,

Push sticks/blocks Save Fingers
~~~~~~~~~~~~~~~~~~~
"The true measure of a man is how he treats someone who can do him absolutely no good."
attributed to Samuel Johnson
~~~~~~~~~~~~~~~~~~~
PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.